CA 02317932 2001-05-04
APPARATUS AND KIT FOR COUPLING
A SNOWMOBILE SUSPENSION
Field of Invention
This invention relates to snowmobile suspension systems, and more particularly
to
uncoupled suspension systems, and even more particularly to an apparatus, in
the form of an
after-market, upgrade kit, to convert an uncoupled suspension system to a
coupled suspension
system.
Background of the Invention
Tracked vehicles such as snowmobiles have rear suspension systems generally
consisting of front and rear suspension arms pivotally mounted on shafts,
which are rotatably
connected to the frame of the snowmobile. They also include a slide frame,
which comprises a
pair of laterally spaced apart slide rails or longitudinal skids
interconnected transversely on
opposing lateral sides of the machine. The slide rails are in sliding contact
with an endless belt
which contacts the snow surface contact drives the snowmobile. Front and rear
suspension arms
pivotally interconnect the chassis to the slide frame.
It is generally known in the art that independent movement of the front and
rear
suspension arms is less desirable than a suspension system in which the front
and rear suspension
arms are coupled. In an uncoupled suspension system, when the front suspension
arm deflects as
it contacts a bump, the independent rear suspension arms remains in its ride
or fully extended
position. This results in an angle of incidence between the slide rails and
the bump. Unless the
impact is so large that it compresses the rear suspension arm spring and shock
absorber
assembly, thereby flattening the angle of incidence, the slide rails will act
as a ramp forcing the
rear of the snowmobile upward. That is, with the slide rails angled in an
upward incline due to
CA 02317932 2001-05-04
the independent deflection of the front suspension arm, but not the rear
suspension arm, the
snowmobile will hop over the bump, imparting a secondary jolt which increases
in intensity with
the speed of the snowmobile. This secondary jolt also results in a loss of
control and a reduction
the speed of the snowmobile.
On the other hand, a coupled suspension system is one in which, for example,
the
rear portion of the suspension system reacts (i. e., is coupled) to the
compression experienced by
the front portion of the suspension system as the snowmobile passes over a
bump in the terrain.
In effect, the bump is « communicated » to the rear portion of the suspension,
causing the rear
portion to be pulled upward toward the chassis before the rear portion
actually reaches the bump.
This reduces the angle of incidence between the slide rail and the bump, which
thereby reduces
the secondary jolt experienced by the rider. As a result, a coupled suspension
system provides
for an improved ride because the coupled suspension is better suited to adjust
to varying terrain
conditions.
Manufacturers have developed a variety of ways to provide coupled suspension
systems,
1 S which typically involve restricting the amount of longitudinal movement of
the rear suspension
arm. Such system are shown in U.S. Patent Nos. 5,881,834, 5,692,579,
5,667,031, and
5,944,134.
Because a coupled suspension offers a superior ride than an uncoupled
suspension, those
skilled in the art of designing snowmobile suspensions have developed coupling
apparatuses that
may be added, as an after-market upgrade, to suspensions that are not coupled.
2
CA 02317932 2000-09-08
It is therefore the object of this invention to provide an apparatus, in the
form of an
after-market, upgrade kit, :for installation onto an uncoupled snowmobile
suspension system
that, when installed, converts the uncoupled suspension system into a coupled
suspension
system.
It is further an object of the present invention to provide an apparatus, in
the form of
an after-market, upgrade kit, specifically configured to be installed onto the
Arctic Cat ~ line
of snowmobiles.
Summary of the Invention
It is the object of the present invention, therefore, to provide an apparatus
~ and an
after-market, upgrade kit constructed and arranged to be installed onto an
uncoupled
snowmobile suspension system that, when installed, converts the suspension
system into a
coupled suspension system. Specifically, the upgrade kit of the present
invention is
configured to be installed onto the; Arctic Cat ~ line of snowmobiles. The
upgrade kit
includes a pair mounting brackets that are mounted to corresponding slide
rails of the
suspension system, a pair of support rods that each fixedly attach to the
corresponding
mounting bracket, and a paiir of couplers that are pivotally interconnected to
the slide rails by
being pivotally mounted to the support rods.
Other objects and advantages of the present invention will be realized in
accordance
with the following detailed description, appended drawings, and claims.
Brief Description of the Drawings
The various embodiments of the present invention are shown throughout the
drawings, in which:
3
CA 02317932 2000-09-08
Fig. 1 is a perspective view of the preferred embodiment of the apparatus of
the
present invention after assembly but before attachment to the snowmobile
suspension;
Fig. 2 is a plan view of a coupler of the upgrade kit of the preferred
embodiment;
Fig. 3 is an end view of a wring arm tube of the upgrade kit of the preferred
embodiment;
Fig. 4 is a side view of the swing arm tube of Fig. 3;
Fig. SA is a plan view of a flat plate of the upgrade kit of the preferred
embodiment;
Fig. SB is a cross-sectional side view of a flat plate of the upgrade kit of
the preferred
embodiment taken along section line SB-SB;
Fig. 6 is a perspective view of a portion of an Arctic Cat ~ snowmobile
suspension
system without the upgrade; kit installed;
Fig. 7 is a side view of a portion of the Arctic Cat ~ snowmobile suspension
system
of Fig. 6;
Fig. 8 is a perspective view of the upgrade kit of the preferred embodiment
installed
onto the Arctic Cat ~ snowmobile suspension system of Fig. 6;
Fig. 9 is a side view of the upgrade kit installed onto the Arctic Cat ~
snowmobile
suspension system of Fig. 8;
Fig. 10 is a top view of the upgrade kit installed onto the Arctic Cat ~
snowmobile
suspension system of Fig. 8;
Fig. 1 lA is a depiction of the; angle of incidence experienced by the slide
rails as the
snowmobile passes over a bump when the suspension system in uncoupled, i.e.,
the upgrade
kit is not installed; and
Fig. 11B is a depiction of the angle of incidence experienced by the slide
rails as the
snowmobile passes over a bump when the suspension system in coupled, i.e., the
upgrade kit
is installed.
4
CA 02317932 2000-09-08
Detailed Description
Referring now more particularly to the Figures, wherein the same reference
numbers
are used where applicable, the apparatus of the present invention, which is
also referred to as
an upgrade kit, is generally indicated at 5 and is illustrated in Fig. 1.
Generally, the upgrade
kit 5 is constructed and an-anged to be installed onto an uncoupled snowmobile
suspension
system, so that when installed, the suspension system becomes coupled. More
specifically,
the upgrade kit S is configured to be assembled onto the Arctic Cat ~ line of
snowmobiles
that are originally manufactured with uncoupled suspension systems, the
details of which are
described below.
Referring to the Figs. 1-5, the upgrade kit 5 comprises, among other
components, two
couplers 10, two support rods 16, and two mounting brackets 22. Figures 2-4
show each
component separately, and Fig. 1 shows the upgrade kit ~ assembled, but not
attached to the
suspension system. The support rods are hereinafter referred to as swing arm
tubes 16, and
the mounting brackets are hereinafter referred to as flat plates 22. As seen
in Fig. 2, the
couplers 10 are flat oblong elements with essentially circular holes 12 formed
therethrough at
one end and oblong holes 14 formed therethrough at opposite ends thereof.
Couplers 10 are
preferably made of an ultr;~-high molecular weight plastic, but any other
suitable material
may be used, as would be understood by those skilled in the art. The thickness
of the
couplers 10 will vary deper.~ding on the material used, but the thickness is
chosen to provide
suitable stiffness and strength. In the preferred embodiment where ultra-high
molecular
weight plastic is used, the thickness of couplers 10 is approximately 0.5
inches.
The upgrade kit 5 also includes the two swing arm tubes 16, an end view of
which is
illustrated in FIG. 3 and a :;ide view of which is shown in FIG. 4. Swing arm
tubes 16 are
5
CA 02317932 2000-09-08
essentially cylindrical, T-shaped elements with a hexagonal stop flange 18 at
one end. Swing
arm tubes 16 are provided with a. threaded bore 20 dawn the center thereof for
threaded
placement of a bolt 40 therein. Although the bore is shown passing through the
entire swing
arm tubes 16, the bore ca.r~ terminate at an intermediate position therein, as
long as the bore
can accommodate a bolt.
When the upgrade kit 5 is assembled (Fig. 1 ), swing arm tube 16 is inserted
into hole
12 of coupler 10 from an end opposite stop flange 18. The stop 18, which has
an average
outside diameter greater than hole 24, limits the transverse displacement of
coupler 10.
When assembled, the bore of hole:. 12 of couplers 10 are in rotational,
sliding contact with
outer, cylindrical surfaces 30 of tlae swing arm tubes 16. The cylindrical
surfaces 30 are
provided with a relatively smooth surface finish. The swing arm tubes 16 are
preferably
made of a corrosion-resistant, steel alloy material or from steel that has
been appropriately
treated so that it is corrosion resistant.
Referring to Fig. 5, the two :flat plates 22 are oblong elements with three
holes 24, 26,
and 28 formed therethrough. Holes. 26 and 28 are provided with recesses 30, 32
on one side
of plate 22 for receiving the; head of a bolt (not shown), and are used to
mount the plates 22 to
the slide rails 42, which are shown in Fig. 8. Holes 24 receive bolts 25 (Fig.
1), which
engage the threaded bore f.0 of swing arm tubes 16 to thereby fixedly attach
the swing arm
tubes thereto. Preferably, so that they do not add excessive weight to the
snowmobile and so
that they provide sufficient strength to couple the suspension, plates 22 are
made from
aluminum. However, any suitable material may be substituted therefor.
Referring now to Figs. 6 and 7, the couplers 10, swing arm tubes 16, and
aluminum
plates 22 are constructed arid arranged to be assembled and attached to the
sliding rails 42 of
an uncoupled snowmobile suspension system. More specifically, upgrade kit 5 is
configured
to be assembled onto an t~,rctic Cat ~ snowmobile suspension system, the rear
portion of
6
CA 02317932 2000-09-08
which is depicted, without the upgrade kit 5 attached, in Fig. 6. The
suspension system of the
Arctic Cat ~ includes slide rails 42 that are interconnected to the snowmobile
chassis (not
shown) by a rear suspension arm 44. The rear suspension arm 44 is a
trapezoidally-shaped
structure that includes a tra~.nsverse rear upper tube portion 46 and a
transverse rear lower tube
portion 48 that are conneci:ed by tyro tubes 50 and 52. The upper tube portion
46 of the rear
suspension arm is pivotally mounted on a first transverse shaft (not shown)
that is fixedly
attached to the chassis 38. Likewise, the lower tube portion 48 of the rear
suspension arm 44,
which extends downwardl3~ and rearwardly, is pivotally mounted on a second
transverse shaft
(not shown) that is fixedly attached to an end of lower arms 60 by bolts 62.
Lower arms 60,
in turn, are pivotally attached to the corresponding slide rails 42 by bolts
64. A shock
– absorber 70 extends fronn the upper tube portion 46 of the rear suspension
arm 44
downwardly and forwardly to fixedly connect to a lower transverse shaft (not
shown), which
is fixedly attached to slide rails 42. The suspension system further includes
a front
suspension arm (not shown) and a fiont shock absorber (not shown). As is known
in the art,
the Arctic Cat ~ suspension system described and shown above is uncoupled.
That is, the
front and rear suspension arms move independently from one another.
Referring now to Figs. 8-10, the attachment of upgrade kit 5 to the Arctic Cat
suspension system will now be described. Flat plates 22 are attached to the
interior of the
snowmobile slide rails 42 on either aide of the suspension, rearward of lower
arms 60. In the
preferred embodiment, the flat plates 22 are fixedly attached to slide rails
42 by being bolted
thereto with bolts 80 that p~~ss through corresponding through holes provided
in slide rails 42.
Bolts 80, nuts and lock washers (not shown) engage holes 26, 28 provided in
flat plates 22.
Bolts 80 may also be the Name bolts used to mount a track adjuster (not
shown), which is
mounted exteriorly on either side of the slide rails 42, as is known in the
art. Although shown
being bolted to the slide rails, the flat plates could also be fixedly
attached thereto by other
7
CA 02317932 2000-09-08
fastening mechanisms, such as welding or brazing. Additionally, flat plates 22
could be
integrally formed with slidt~ rails 42, rather than being separate, distinct
elements.
The plastic couplers 10 are pivotally interconnected to the flat plates 22 via
swing arm
tubes 16. Each swing army tube 16. is inserted into hole 12 of plastic
couplers 10, with the
stop flange 18 facing the interior of the suspension system, and fixedly
connected to flat plate
22 with bolts 82 and lock washers 83 (Fig. 1). Each cylindrical, swing arm
tube 16 thus
provides a pivot point for plastic couplers 10 to rotate. Because the length
of each swing arm
tube 16 is greater than the thickness of the plastic couplers 10, as best seen
in Fig. 10, the
plastic couplers can also slidingly translate in the transverse direction on
the cylindrical
surface 30 of swing arm tribes 16. The plastic couplers 10 are then connected
to the rear
swing arm 44 by removing bolt 62 ;end rotating lower arm 60 so that a free end
of tube 48 is
exposed. Each plastic coupler 10 is slipped over tube 48 through oblong slot
14, and the rear
swing arm 44 is reattached to lower arm 60.
Once assembled, thf; plastic couplers 10 couple the suspension system to
improve the
ride of the snowmobile. Prior to the installation of the upgrade kit, when the
snowmobile hits
a bump, as depicted in Fig. 11 A, the front of the slide rail compresses
before the rear of the
slide rail, and as the slide rails 42 move upward the rear suspension arm 44
pivots about a
shaft (not shown) fixedly attached b;y bolts 62. At the same time, lower arm
60 freely pivots
about bolt 64, and this pivoting movement of lower arm 60 is not limited in
either rotation
direction. Since lower arm 60 in unrestrained from rotational movement, the
suspension
system, without the upgrade. kit installed, is uncoupled. That is, as the
front of the rails hits a
bump, the front of the rails rise but the rear of the rails are still at the
bottom of the bump,
causing the rail to be presented at a specific angle of incidence 90 as the
rear of the rail
approaches the bump. The l;reater this angle of incidence is, the more
secondary kick there is
8
CA 02317932 2000-09-08
to the rider when the rear hits the bv.unp and the greater the loss of control
there is to the rider,
and the greater loss of speed of the vehicle.
With the upgrade kit 5 installed, as the front of the slide rails rise,
causing rotational
movement of the rear suspension arm 44 and lower arms 60, the lower arms 60
are restrained
from freely rotating due to the limitation imposed on it by plastic couplers
10. For example,
as the lower arm 60 rotates clockwise as shown in Fig. 6, it engages the
forward end 84 of
slots 14 and imparts a pulling force to the plastic coupler 10. Since plastic
couplers 10 are
interconnected to the slidE: rails 4:2, the rear of slide rails 42 are
correspondingly pulled
upward, as shown in Fig. 11 B. Thus, the suspension system becomes « front to
rear coupled »
with the upgrade kit installed. That is, as the front of the suspension hits a
bump, the front
« communicates » with the rear and i:orces (or pulls) the rear upward prior to
the rear actually
hitting the bump. This causes the rail to be presented at a specific angle of
incidence 92 as
the rear of the rail approached the bump, where the angle of incidence 92
(with coupling) is
less than the angle of incidence 90 (without coupling). This reduction in the
angle of
incidence as a result of the system being coupled with upgrade kit 5 reduces
secondary kick,
provides more control to the rider, and minimizes the loss of speed as the
snowmobile passes
over the bump.
Similarly, with the upgrade kit installed, the suspension system becomes « rear
to
front » coupled. Where the rider lands on the back of the snowmobile, after the
rear
suspension arm 44 has displaced the’ length of slot 14 to the rear, due to the
counterclockwise
rotation of lower arm 60 as shown in Fig. 6, further movement and rotation are
prevented by
the lower tube’s 48 engagement with a rearward end 86 of slot 14. This stopped
travel in the
rear suspension arm 44 cau;>es the front suspension arm (not shown), and thus
the front of the
slide rails, to start to displace upward. Thus, the suspension system becomes
coupled from
the rear to the front. Without the upgrade kit 5 installed, where the rider
lands on the back of
9
CA 02317932 2000-09-08
the snowmobile, the front suspension arm is independent of the rear arm and
only the rear
suspension arm 44 collapses.
Though not intended to be limiting, the dimensions of the components of
upgrade kit
5, which are sized for the P~rctic Cat ~ line of snowmobile suspensions, are
the following:
Table 1: Dimensions of upgrade kit components.
Plastic Couplers 10 (Fig. 2) dimension (inches)
L 1 2.875
L2 0.750
D 1 0.875
D2 1.000
R1 1.000
Swing arm tubes 16 (Fig. 4)
L3 1.000
L4 0.100
D3 0.875
Flat plates 22 (Figs., SA, SB;I
LS 1.500
L6 1.813
L7 1.250
D4 0.437
DS 0.250
D6 0.750
The upgrade kit 5 with the above dimensions is intended for the following
Arctic Cat ~ snowmobile models: the Z 440 (model years 1998 and 1999); the
entire ZL
series (model years 1998-2.000); the entire ZR series (model years 1997-2000);
the entire
ZRT series (model years 1997-2000); the Thunder Cat (model years 1998-2000);
the Cougar
DLX (model year 1998 only); and the EXT, EFI, DLX, and 600 (model year 1998
only).
CA 02317932 2000-09-08
However, as would be understood by those skilled in the art, there are
potentially other
snowmobile suspensions o,n which the present invention may be used.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiments, it is to be
understood that the
invention is not to be limited to the disclosed embodiments and elements, but,
to the contrary,
is intended to cover various modifications, combinations of features,
equivalent
arrangements, and equivalent elements included within the spirit and scope of
the appended
claims. Furthermore, the dimensions of features of various components provided
are not
meant to be limiting, and tlae size of the components can vary from the size
that is portrayed
in the figures and table herein in order to accommodate differently sized
suspension system
components.
English
